The present invention relates to a collation system of a fingerprint card such as the Ten Print Card, and particularly to a method of and an apparatus for pre-selecting fingerprint card having certain similarity to an S-card to be identified among a plurality of F-cards registered in a data base in order to reduce number of fingerprint cards to be subjected to fine verification.
Consider a case where a fingerprint card including fingerprint images of fingers obtained from a specific person (hereafter called a search card, or a S-card) is verified whether there is a fingerprint card of the same person in a large scale database wherein a number (M) of fingerprint cards (hereafter called filed cards, or F-cards), each taken from each of M persons and having the same format with the S-card, are registered.
As for verification method of identity between a pair of fingerprint images, a method making use of minutia verification is well known and disclosed, for example, in a Japanese patent published with specification No. 34508/'88. By way of the above minutia verification apparatus, a card having identity with the S-card can be retrieved in the F-cards with sufficient precision, by repeating the minutia verification of each of ten fingerprint images of the S-card for each of ten fingerprint images of each of the F-cards. However, it takes a lot of computational time when M is large, needing M.times.(average valid finger number/card) times of the minutia verification.
Therefore, it is effective for reducing total computational time to reduce number of F-cards to be finely verified by way of a pre-selection, wherein certain feature data extracted from each fingerprint pattern of each of the F-cards are compared to feature data extracted from each respective fingerprint pattern of the S-card, and only F-cards of feature data having a certain similarity to those of the S-card are selected to be processed with the fine verification, other discordant F-cards being rejected without performing the fine verification.
Hereafter, this procedure to determine a set of the F-cards, whereof coincidence to the S-card is to be finely verified, will be called the pre-selection.
For realizing the pre-selection, an apparatus is disclosed by us in a Japanese patent application laid open as a Provisional Publication No. 114981/'97, wherein a similarity value between two fingerprint cards is estimated by comparing pattern level classification and sub-pattern level features of each of ten fingerprint patterns between the two fingerprint cards, and accordance/discordance of the two fingerprint cards is determined by comparing the similarity value to a threshold value.
FIG. 6 is a block diagram illustrating configuration of this apparatus.
In the prior art apparatus of FIG. 6, data of pattern level classifications and sub-pattern level features of ten fingerprints of each of M sheets of the F-cards are obtained by a fingerprint pattern classification unit 95 and a fingerprint feature extraction unit 97 from an external image memory 92, and prepared in a F-side card feature storing section 93.
When data of an S-card is input, a fingerprint pattern classification unit 96 and a fingerprint feature extraction unit 98 extract data of the pattern level classification and the sub-pattern level features of the S-card in the same way for storing them in an S-side card feature storing section 94.
For the pre-selection, the data of the S-card and data of each of the F-cards are input to a fingerprint card selection unit 91, which calculates the similarity value between them and determines whether the concerning F-card is to be processed with the fine verification or not by comparing the similarity value to a predetermined threshold value. By repeating above procedure for data of every of M sheets of the F-cards, the pre-selection is performed. Since the calculation amount necessary for the pre-selection is far smaller than that necessary for the fine verification of the F-cards rejected by the pre-selection, total calculation amount for identifying the S-card can be considerably reduced, enabling a remarkable high-speed processing.
However, in the prior art apparatus of FIG. 6, the similarity value estimation is performed by the fingerprint card selection unit 91 successively for data of every of M sheets of F-cards, which takes still a certain computational time and a large calculation ability is required even for performing the pre-selection when number M of F-cards becomes large.